why I only get a clearcase version 0?

Normally, the first committed version should start from 1. Version 0 is identical with branch point. But now I got a only version 0, and this prevent me to checkin any other version coz it warned me that the branch already created.

As explained in "Before adding files and directories to source control", the version 0 is a placeholder marking the start for all versions in a given branch:

You can end up with only the version 0 when you undo-checkout a file you just checked out in a new branch (in that case, only a version 0 for the newly created branch remains).

Regarding branches, you can have error like "element already has a branch of type branch", but only when there is an issue with the server and client time (clock) being not in sync.

ClearCase creates version 0 when you create an element (or a branch), which is usually checked out automatically. Version 0 is always either empty, or same as the branched version, as you noted. There shouldn't be any problem simply checking in version 1 on top of it.

Note that branches are created when you check out, not when you check in, so you shouldn't get any warnings on check-in. If you post the exact command line and warnings/errors, we'll probably be able to help you out more.

It could perhaps be that you've created a new element on your branch, and you're missing "/main/0 -mkbranch" in your config spec.

HTH.